COMMISSION 27 OF THE I. A. U.
              INFORMATION BULLETIN ON VARIABLE STARS
                             NUMBER 20

                                          Konkoly Observatory
                                          Budapest
                                          7 February 1963


              UNUSUAL NEW VARIABLE S 7901 CYGNI

            AR =20h21m.9      Decl. = + 53deg 18'       1855.0
                20 23 .1              + 53    27        1900.0


                       [FIGURE 1]


When comparing 2 plates 1953 March 20/Sep 3 from the Zeiss-Triplet 
170/1200 mm, centered at 33 Cygni, I found a star with a
rapid variability of about 1mag.5, giving at first sight the
impression of a Cluster type variable. As this occured on the 19. pair
of plates compared, the probability that such an object might have
escaped discovery was very small. The further investigations on more
than 350 plates had a surprising result: The full range variations
from 14mag.8 to 16mag.5, often from one day to the other, are only
shown in March and April, 1953  (16 plates). The star is faint on a 
single plate of Jan. 13/14, 1953, and a few minima with a range of
1mag are observed in May and June, but no variability in 1952 (31
plates) and in the second half of the year 1953 (35 plates). From
Dec. 6, 1961, to Dec. 2, 1962, there are 107 plates taken with the
new Zeiss Astrograph 400/1600 mm, showing  only very rare slight
variations with a range of scarcely more than 0mag.2, the star being
generally at maximum light. No plates are available from the years 
1932, 35-38, 40-42, 55-57.

There is no doubt that the variable belongs to the RW Aurigae type. It
is known that the variability of these stars can be temporarily interrupted 
at any brightness, but as to the extent of these periods the new
variable seems to be unique.

Attention may be drawn in this connection to some stars mentioned 
in the catalogues as invariable, having been announced as
variables, even by experienced investigators, but never being confirmed
(RW Aql as an example). It seems not improbable that at least some of
these objects are of the type of S 7901 Cyg.


                                            C. HOFFMEISTER
                                        Sonneberg Observatory